Thermoplastic resin film and label paper employing the same

ABSTRACT

A thermoplastic resin film (i) which has a degree of dimensional change through heating and cooling (α) in the range of from −2% to 2% as measured by thermomechanical analysis in the range of from room temperature to 135° C., or which has a degree of thermal shrinkage of 1.8% or lower upon heating at 130° C. for 30 minutes or longer; and a label paper employing the same. The label paper has suitability for heated-roll fixing type electrophotographic printers and is satisfactory in curling after printing.

TECHNICAL FIELD

[0001] The present invention relates to a thermoplastic resin film whichhas a degree of dimensional change through heating and cooling (α) inthe range of from −2% to 2% as measured by thermomechanical analysis inthe range of from room temperature to 135° C., or which has reducedthermal shrinkage upon heating at 130° C. for 30 minutes or longer. Theinvention further relates to a label paper which employs the film andwhich has reduced curling after being printed with a printing method inwhich thermal energy is applied, in particular, printing with aheated-roll fixing type electrophotographic printer.

BACKGROUND ART

[0002] Thermoplastic resin films which have satisfactory waterresistance, in particular, polyolefin-based synthetic papers, may beused, for example, as stickers for outdoor advertising or as labelswhich may be applied to containers for frozen foods, because theconventional stickers, and the coated paper used in such labels, havepoor water resistance.

[0003] Resin films for use in water resistant labels are known. Withrespect to details thereof, reference may be made to, for example, suchfilms are described in Examined Japanese Patent Publications Nos.46-40794 and 49-1782, Unexamined Published Japanese Patent ApplicationsNos.56-118437, 57-12642, and 57-56224, etc.

[0004] However, such polyolefin-based synthetic papers, when used aslabels and printed with a heated-roll fixing type electrophotographicprinter, in which the heated roll has a surface treatment as high as 140to 190° C., have a higher degree of thermal shrinkage than the releasepaper adhered thereto, which causes the label to curling considerablyafter printing. In extreme cases, the label paper may roll up into acylinder, making it difficult to peel the printed synthetic paper fromthe release paper. Because of this curling problem, polyolefin-basedsynthetic papers cannot be satisfactorily printed using a heated-rollfixing type electrophotographic printer.

[0005] An object of the present invention is to provide a thermoplasticresin film, and a label papers comprising such a film, which has reducedthermal curling compared with conventional papers, and can be easilypeeled from the release paper when used as a label printed with aheated-roll fixing type electrophotographic printer.

DISCLOSURE OF THE INVENTION

[0006] The thermoplastic resin film (i) of the present invention may beused as a base paper for labels, and has a degree of dimensional changeupon heating and cooling (α) in the range of from −2% to 2%, as measuredby thermomechanical analysis in the range of from room temperature to135° C., or which has a degree of thermal shrinkage of 1.8% or lowerupon heating at 130° C. for 30 minutes or longer. A label prepared fromthis film comprises a label paper comprising the thermoplastic resinfilm of the present invention, a pressure-sensitive adhesive, and arelease paper. The label of the present invention has reduced curlheight after printing with a heated-roll fixing type electrophotographicprinter, and is therefore suitable for use with this printing method.

[0007] The invention directed attention to the relationship between thethermal dimension change of label papers and the curling thereof inorder to solve the problems described above, and the above object isaccomplished by regulating the thermal dimensional change of labelpapers comprised of the thermoplastic resin film of the presentinvention, to a specific value. Namely, a reduction in curl height andsatisfactory printing properties have been achieved by using athermoplastic resin film as a label paper which has a degree ofdimensional change (α) in a specific range, and/or a specific degree ofthermal shrinkage.

BEST MODE FOR CARRYING OUT THE INVENTION

[0008] The thermoplastic resin film (i) of the present invention has areduced degree of dimensional change upon heating and cooling (α) asmeasured by thermomechanical analysis in the range of from roomtemperature to 135° C., and/or a reduced degree of thermal shrinkageupon heating at 130° C. for 30 minutes or longer. The present inventionfurther relates to a label paper comprising the film and, bondedthereto, a pressure-sensitive adhesive layer (ii) and a release paper(iii). The present invention will be explained below in detail.

[0009] (1) Thermoplastic Resin Film (i)

[0010] The thermoplastic resin used in the thermoplastic resin film (i)of the present invention may include, for example, polyolefin resinssuch as ethylene-based resins, e.g., high-density polyethylene andmedium-density polyethylene, and propylene-based resins, poly(4-methyl-1-pentene), ethylene/cycloolefin copolymers, polyamide resinssuch as nylon-6, nylon-6,6, nylon-6,10, nylon-6,12, and nylon-6,T,thermoplastic polyester resins such as poly(ethylene terephthalate) andcopolymers thereof, poly (ethylene naphthalate), and aliphaticpolyesters, and thermoplastic resins such as polycarbonates, atacticpolystyrene, syndiotactic polystyrene, and poly (phenylene sulfide).These resins may be used as a mixture of two or more thereof. Polyolefinresins are the preferred resin. Propylene-based resins are the preferredpolyolefin resin, based, for example, on their good chemicalresistance,- and low cost.

[0011] The propylene-based resin may include an isotactic orsyndiotactic propylene homopolymer or a propylene homopolymer having anyof various degrees of stereoregularity, or a copolymer having propyleneas the main component, with one or more α-olefin comonomers such asethylene, butene-1, hexene-1, heptene-1, and 4-methyl-1-pentene. Thiscopolymer may be a binary system, ternary system, or quaternary system,and may be a random copolymer or block copolymer.

[0012] The thermoplastic resin may also be blended with fine inorganicparticles to form the thermoplastic resin film (i). The fine inorganicparticles may include, for example, particles of calcium carbonate,calcined clay, silica, diatomaceous earth, talc, titanium oxide, bariumsulfate, alumina or the like, which have an average particle diameter offrom 0.01 to 15 μm.

[0013] If the thermoplastic resin film is a polyolefin resin film, thepolyolefin may be blended with fine organic particles. The fine organicparticles may have a melting point of from 170 to 300° C. higher thanthe melting point of the polyolefin resin, or a glass transitiontemperature of from 170° C. to 280° C. higher than the melting point ofthe polyolefin resin.

[0014] For example, the fine organic particles may include particles ofpoly (ethylene terephthalate), poly(butylene terephthalate), apolycarbonate, nylon-6, nylon-6,6, nylon-6,T, a polymer of acycloolefin, or the like.

[0015] Fine inorganic particles are preferred to organic fine particlesbecause of their lower cost. Calcium carbonate, calcined clay, and talcare especially preferred inorganic fine particles.

[0016] As needed, the thermoplastic resin film may also include astabilizer, light stabilizer, dispersant, lubricant, and the like. Theamount of stabilizer incorporated into the thermoplastic resin film maybe from 0.001 to 1% by weight, based on the total weight of thethermoplastic resin. The stabilizer may include, for example, asterically hindered phenol, phosphorus, or amine compound or the like.The amount of light stabilizer incorporated into the thermoplastic resinfilm may be from 0.001 to 1% by weight, based on the total weight of thethermoplastic resin. The light stabilizer may include, for example, asterically hindered amine, benzotriazole, or benzophenone compound orthe like. In addition, a dispersant for the fine inorganic particles mayalso be added, including for example a silane coupling agent, a higherfatty acid such as oleic acid or stearic acid, a metal soap,poly(acrylic acid), poly(methacrylic acid), salts thereof, or the like.The amount of dispersant may be from 0.01 to 4% by weight, based on thetotal weight of the thermoplastic resin.

[0017] The thermoplastic resin film (i) may have one or more layers. Forexample, the thermoplastic resin film (i) may be a single layer film, ormay have a two-layer structure composed of a base layer and a surfacelayer, a three-layer structure having a surface layer on each of thefront and back sides of a base layer, or a multilayer structurecomprising a base layer, a surface layer, and one or more other resinfilm layers interposed therebetween. The film may comprises from 35 to100% by weight thermoplastic resin and from 65 to 0% by weight inorganicand/or organic fine particles.

[0018] If the thermoplastic resin film (i) is a single-layer polyolefinresin film and contains inorganic and/or organic fine particles, it maycomprise from 35 to 99.5% by weight of a polyolefin resin and from 65 to0.5% by weight of the inorganic and/or organic fine particles, andpreferably comprises from 50 to 97% by weight polyolefin resin and from50 to 3% by weight of the inorganic and/or organic fine particles. Ifthe thermoplastic resin film has a multilayer structure comprising abase layer and a surface layer each containing inorganic and/or organicfine particles, the base layer of the thermoplastic resin film maycomprise from 35 to 99.5% by weight of a polyolefin resin aid from 65 to0.5% by weight of the inorganic and/or organic fine particles and thesurface layer may comprise from 25 to 100% by weight of a polyolefinresin and from 75 to 0% by weight of the inorganic and/or organic fineparticles. In this case, the base layer preferably comprises from 50 to97% by weight of a polyolefin resin and from 50 to 3% by weight of theinorganic and/or organic fine particles and the surface layer preferablycomprises from 30 to 97% by weight of a polyolefin resin and from 70 to3% by weight of the inorganic and/or organic fine particles.

[0019] In order to improve the flexibility of the film, the amount ofthe inorganic and/or organic fine particles incorporated into the baselayer in a single-layer film or a multilayer film structure ispreferably 65% by weight or smaller. If the film is to be made by aprocess which includes stretching the film, described below, the amountof the inorganic and/or organic fine particles in the surface layer ispreferably 75% by weight or less, in order that the stretched film havea higher level of surface strength.

[0020] Formation of the Resin Film

[0021] The method of making the thermoplastic resin film (i) of thepresent invention is not particularly limited, and any of various knowntechniques may be used. For example, the thermoplastic resin film may bemade by extruding a molten resin into a sheet form with a single-layeror multilayered T-die or I-die, connected to a screw type extruder, orby calendering, rolling, inflation, by casting or calendering a mixtureof a thermoplastic resin and an organic solvent or oil and subsequentremoving the solvent or oil, casting a solution of a thermoplastic resinand removing the solvent, and the like. In order to efficiently obtain afilm having a large area, a combination of any of the above film formingmethods with the stretching treatment described below, is preferred.

[0022] Stretching

[0023] Various known methods may be used for stretching, and may becarried out in a temperature range known to be suitable for thethermoplastic resin used. If the resin is a noncrystalline resin, thestretching temperature is not lower than the glass transition point ofthe thermoplastic resin. If the resin is crystalline, the stretchingtemperature range may be from the glass transition point of thenoncrystalline portions of the resin to the melting point of thecrystalline portions. Examples of methods for stretching films include,for example, machine-direction stretching utilizing a difference inperipheral speed between rolls. transverse-direction stretching with atenter oven, calendering, simultaneous biaxial stretching with acombination of a tenter oven and a linear motor, and the like.

[0024] The stretch ratio is defined as the area of the film afterstretching, divided by the area of the film prior to stretching. Thestretch ratio is not limited to any particular value, and is selectedbased on the desired properties of the thermoplastic resin. For example,if the thermoplastic resin is polypropylene or a copolymer thereof, theunidirectional stretch ratio may be from about 1.2 to about 12,preferably from 2 to 10, and the biaxial stretch ratio may be from about1.5 to about 60, preferably from 10 to 50. If other thermoplastic resinsare used, the unidirectional stretch ratio may be from 1.2 to 10,preferably from 2 to 5, and that in biaxial stretch ratio is from 1.5 to20, preferably from 4 to 12. If desired, the film may also be heattreated at a high temperature.

[0025] The stretching temperature is lower than the melting point of thethermoplastic resin by from 2 to 150° C., preferably from 2 to 60° C.,and is selected based on the stretching process used. For example, ifthe thermoplastic resin is a propylene homopolymer or copolymer (meltingpoint, 155 to 167° C.), high-density polyethylene (melting point, 121 to134° C.), or poly (ethylene terephthalate) (melting point, 246 to 252°C.), the stretching temperature may be in the range of from 110 to 164°C., from 110 to 120° C., or from 104 to 115° C., respectively.

[0026] Furthermore, the stretching speed may be from 20 to 350 m/min.

[0027] If the thermoplastic resin film is made from a polypropylenehomopolymer using a process comprising a transverse-direction stretchingstep using a tenter oven, an effective technique for reducing the degreeof thermal shrinkage is to dispose a heat-setting zone in the latterhalf of the process and heat the stretched and formed polypropylene filmto a temperature which is at most close to its melting temperature. Thetemperature of the heat-setting zone can any of a wide range oftemperatures, which depends on the line speed of the film during thestretching step, the flow speed and flow rate of the high-temperatureair blown in the heat-setting zone, the structure of the heat-settingzone, etc. For example, the temperature of the heat setting zone may bein the range of from 158 to 175° C.

[0028] If the thermoplastic resin film contains fine inorganic particlesor an organic filler, the film surfaces may also develop microcracks andinner portions of the film may develop microvoids.

[0029] After the stretching, the thermoplastic resin film may have athickness in the range of from 30 to 350 μm, preferably from 50 to 300μm.

[0030] Heat Treatment

[0031] Usually, a combination of the forming and stretching processdescribed above, together with high-temperature setting in aheat-setting zone or a heat treatment after the forming, provides ameans for regulating the thermoplastic resin film (i) of the inventionso that the degree of dimensional change through heating and cooling (α)of the film, as measured by thermomechanical analysis in the range offrom room temperature to 135° C., is from −2% to 2%, preferably from−1.5% to 1.5%, more preferably from −1.2% to 1.2%, and/or the degree ofthermal shrinkage of the film upon heating at 130° C. for 30 minutes is1.8% or lower, preferably 1.5% or lower, more preferably 1.2% or lower.

[0032] The heating temperature of the heating zone or the heat treatmentis preferably lower than the melting point of the thermoplastic resin,and may be, for example, in the range of from 90° C. to 250° C.,preferably from 95° C. to 250° C., more preferably from 105° C. to 160°C. At temperatures lower than 90° C., the heat treatment tends to havean insufficient effect on the degree of dimensional change or thermalshrinkage. At temperatures exceeding 250° C., the film may deform orbecomes wavy. Furthermore, if the thermoplastic resin is a polypropyleneresin, the heating temperature is preferably in the range of from 90 to175° C., more preferably from 95 to 158° C. even more preferably from105 to 140° C. At temperatures lower than 90° C., either the effect ofthe heat treatment is insufficient, or a long heating time is necessaryin order to obtain a sufficient effect, thereby making it difficult toefficiently produce the film on an industrial scale. The temperature ofa heat conducting medium used for the heating the film is selected sothat the film has a temperature within the range shown above.

[0033] The heating time may be selected over a wide range of times,preferably not shorter than 0.1 second. However. it may be in the rangeof from 2 seconds to 30 days, more preferably from 4 seconds to 7 days,even more preferably from 4 seconds to 2 days. Heating times longer than30 days are apt to result in film deterioration, while heating timesshorter than 0.1 second may provide insufficient treatment. The heattreatment may be carried out after the film itself is formed, or afterthe film is surface treated, discussed below.

[0034] Examples of methods for heat treating the film of the presentinvention include a heat treatment conducted in a high-temperatureheat-setting zone after stretching the film in a tenter oven, asdescribed above, a heat treating the film in sheet or roll form in anoven, heating with high-temperature air, steam, or other heatingconducting media, etc. The heat treatment may be carried out in such amanner that the ends of the film are kept unconstrained so as to allowthe film to gradually shrink upon heating. If the ends of the film arefixed, the heat treatment may be conducted by arranging the devices usedto fixing two opposed ends or for fixing the two pairs of opposed ends,so that the distance therebetween may be reduced in conjunction with thethermal shrinkage of the film. Alternatively, the treatment may beconducted in such a manner that at least two opposed ends of the filmare kept fixed so as not to follow the film shrinkage. Specific examplesinclude a method in which the film in a roll form is heated in aforced-air oven, a method in which the film in the form of either singlesheet or in the form of stacked sheets is heated, a method in which thefilm is heated by contact with at least one high-temperature roll, etc.

[0035] Surface Treatment

[0036] The thermoplastic resin film (i) is preferably subjected to asurface treatment on at least the side of the film which is intended tobe printed, or on both sides, for the purpose of improving toneradhesion, improving the adhesion of a toner-receiving layer on thethermoplastic resin film (i), or imparting antistatic properties.

[0037] Such surface treatments may include, for example, a surfaceoxidation treatment, a combination of a surface oxidation treatment anda coating of a surface-treating agent, etc. Conventional treatments forfilms, either alone or in combination, such as corona dischargetreatment, flame treatment, plasma treatment, glow discharge treatment,and ozone treatment may be used as the surface oxidation treatment.Corona treatment and flame treatment are preferred. If corona treatmentis used, the amount of treatment should be from 600 to 12,000 J/m² (from10 to 200 W-min/m²), preferably from 1,200 to 9,000 J/m² (from 20 to 180W-min/m²), and if flame treatment is used, the amount of treatmentshould be from 8,000 to 200,000 J/m², preferably from 20,000 to 100,000J/m².

[0038] A surface-treating agent may consists mainly of one ingredient ora mixture of two or more ingredients selected from the following primersand antistatic polymers. In order to obtain good toner adhesion andantistatic properties, the preferred surface-treating agents are primersand combinations of one or more primers with one or more antistaticpolymers.

[0039] (1) Primers

[0040] The primer may be, for example, polyethyleneimine type polymerssuch as polyethyleneimine, polyethyleneimines modified with an alkylgroup having 1 to 12 carbon atoms, poly(ethyleneimine-urea)ethyleneimine adducts of polyamine-polyamides, and

[0041] epichlorohydrin adducts of polyamine-polyamides, acrylic esterpolymers such as acrylamide/acrylic ester copolymers, acrylamide/acrylicester/methacrylic ester copolymers, polyacrylamide derivatives, acrylicester polymers containing oxazoline groups, and poly(acrylic esters),water-soluble resins such as polyvinylpyrrolidone, polyethylene glycol,poly(vinyl alcohol); water-dispersible resins such as poly (vinylacetate), polyurethanes, ethylene/vinyl acetate copolymers,poly(vinylidene chloride), chlorinated polypropylene, andacrylonitrile/butadiene copolymers, and the like.

[0042] Polyethyleneimine type polymers, urethane resins, poly(acrylicesters), and the like are preferred primers. Polyethyleneimine typepolymers are more preferred, and polyethyleneimine having a degree ofpolymerization of from 20 to 3,000, ethyleneimine adducts ofpolyamine-polyamides, and modified polyethyleneimines obtained bymodifying these polymers with halogenoalkyl, halogenoalkenyl,halogenocycloalkyl, or halogenobenzyl groups having 1 to 24 carbonatoms, are most preferred.

[0043] (2) Antistatic Polymers

[0044] Examples of antistatic polymers include cationic, anionic,amphoteric, and other polymers. Examples of cationic polymers includepolymers having a quaternary ammonium salt structure or a phosphoniumsalt structure, nitrogen-containing acrylic polymers, and acrylic ormethacrylic polymers having nitrogen as a quaternary ammonium saltstructure. Examples of the amphoteric polymers includenitrogen-containing acrylic or methacrylic polymers having a betainestructure. Examples of the anionic polymers include styrene/maleicanhydride copolymers or alkali metal salts thereof, alkali metal saltsof ethylene/acrylic acid copolymers, alkali metal salts ofethylene/methacrylic acid copolymers, and the like. Acrylic ormethacrylic polymers having nitrogen as a quaternary ammonium saltstructurc are especially preferred.

[0045] An antistatic polymer having any desired molecular weight may beobtained by regulating the polymerization conditions under which it ismade, for example, the polymerization temperature, the kind and amountof a polymerization initiator, the amount of a solvent used, and thepresence of a chain transfer agent. In general, the antistatic polymershould have a molecular weight (M_(w)) of from 1,000 to 1,000,000preferably 1,000 to 500,000.

[0046] The surface-treating agent described above for use in the presentinvention may contain the following optional ingredients, as needed.

[0047] (3) Optional Ingredient 1: Crosslinking Agent

[0048] Coating film strength and water resistance can be furtherimproved by adding a crosslinking agent. Examples of the crosslinkingagent may include, for example, epoxy compounds such as a glycidyl etherand a glycidyl ester, and aqueous dispersion type resins such as epoxyresins and isocyanate, oxazoline, formalin, and hydrazide compounds. Theamount of the crosslinking agent added to the surface-treating agent maybe in the range of up to 100 parts by weight per 100 parts by weight ofthe effective ingredients of the surface-treating agent, which excludethe solvent.

[0049] (4) Optional Ingredient 2: Alkali Metal Salt or Alkaline EarthMetal Salt

[0050] Examples of the alkali metal salt or alkaline earth metal saltmay include water-soluble inorganic salts such as, e.g., sodiumcarbonate, sodium hydrogen carbonate, potassium carbonate, sodiumsulfite, and other alkaline salts, and further may include sodiumchloride, sodium sulfate, sodium nitrate, sodium tripolyphosphate,sodium pyrophosphate, and ammonium alum.

[0051] The amount of optional ingredient 2 may be 50 parts by weight orsmaller per 100 parts by weight of the effective ingredients of thesurface-treating agent, which exclude the solvent.

[0052] (5) Optional Ingredients 3

[0053] The surface-treating agent may further contain a surfactant, anantifoamer, a water-soluble or water-dispersible, finely particulatesubstance, and other processing aids.

[0054] The amount of optional ingredients 3 may be 20 parts by weight orsmaller per 100 parts by weight of the effective ingredients of thesurface-treating agent, which exclude the solvent.

[0055] Formation of Surface Treatment Layer

[0056] The ingredients for the surface treatment layer described aboveare typically as a solution, for example by dissolving them in water ora hydrophilic solvent such as methyl alcohol, ethyl alcohol, orisopropyl alcohol. Preferably, the ingredients are used in the form ofan aqueous solution. The total concentration of these ingredients in thesolution is, for example, about from 0.1 to 20% by weight, preferablyabout from 0. to 10% by weight, based on the total weight of thesolution.

[0057] The surface treatment layer is coated onto the thermoplasticresin film (i) by coating the solution with a roll coater, blade coater,bar coater, air-knife coater, size press coater, gravure coater, reversecoater, die coater, lip coater, spray coater, or the like. Smoothing ofthe surface treatment layer is carried out as needed, and any excesswater or hydrophilic solvent is removed by a drying step.

[0058] The solution may be applied in an amount of from 0.005 to 5 g/m²,preferably from 0.01 to 2 g/m², based on the weight of the dried film.

[0059] If the thermoplastic resin film (i) is a stretched film, thesurface treatment layer may be provided by a single-stage coating ormultistage coating process, either before or after the machine- ortransverse-direction stretching.

[0060] Properties of Thermoplastic Resin Film (i)

[0061] If the thermoplastic resin film has been stretched, thethermoplastic resin film has a porosity, as shown by the followingequation, of from 5 to 60%, preferably from 8 to 35%, more preferablyfrom 8 to 30%. If the porosity of the film is lower than 5%, it isdifficult to reduce the weight of the film. Porosities exceeding 60% areapt to result in poor label strength.${{Porosity}\quad (\%)} = {\frac{\rho_{0} - \rho}{\rho_{0}} \times 100}$

[0062] ρ₀: density of the resin film before stretching

[0063] ρ: density of the resin film after stretching

[0064] The density of the film as measured in accordance withJIS-P8118-1976, and may be in the range of from 0.65 to 1.3 g/cm³,preferably from 0.8 to 1.1 g/cm³. Films with densities lower than 0.65g/cm³ tend to have poor base strength. If the density of the filmexceeds 1.3 g/cm³, a stack of many sheets may be too heavy to carry.

[0065] Furthermore, the film should have the following properties: theopacity as measured in accordance with JIS-P8138-1976 should be from 20to 100%, preferably from 60 to 100, and the Bekk's surface smoothnessshould be from 50 to 25,000 seconds.

[0066] Thermomechanical Analysis

[0067] The degree of dimensional change after heating and cooling (α) asmeasured by thermomechanical analysis (hereinafter abbreviated as “TMA”)in the range of from room temperature to 135° C. (hereinafterabbreviated as “degree of dimensional change (α)”) of the thermoplasticresin film (i) of the present invention should be in the range of from−2 to 2%.

[0068] The thermomechanical analysis of the films of the presentinvention may be conducted with a commercial thermomechanical analyzer.Typical examples of the apparatus, principle, features, and uses aredescribed in documents including “1997 Bunseki Kiki Soran”, edited andpublished by Japan Analytical Instruments Association, Chap. IV, p. 92(Sep. 1, 1997) and Bernhard Wunderlich, “Thernal Analysis”, Chap. 6, pp.311-312, Academic Press, Inc., 1990, herewith incorporated by reference.

[0069] Specific examples of the TMA apparatus include a “TMA120C”manufactured by Seiko Instruments Inc., a “TMA7” manufactured byPerkin-Elmer Corp., a “TMA-50” manufactured by Shimadzu Corp., a“TM-9200” manufactured by Shinku Riko, and the like.

[0070] An example of a method for measuring the degree of dimensionalchange after heating and cooling by TMA of a film according to thepresent invention is as follows. A TMA apparatus, e.g., “TMA120C”manufactured by Seiko Instruments Inc., was used in the tension mode. Afixed load selected in the range of from about 1 to 20 g was used. Afilm sample having a width of 4 mm and a length of 10 mm (excluding theportions fixed to the upper and lower clamps of the TMA) was preparedand affixed to the TMA. The rate of heating and that of cooling duringeach measurement was 2° C./min. The samples were heated in a measuringtemperature range, i.e. from room temperature. e.g., 25° C. to 50° C. toa set temperature of 150° C. (actual temperature, 135° C.) and thencooled back to room temperature. The degree of shrinkage or expansion ofthe sample piece is expressed as a percent of the initial sample lengthof 10 mm, and is referred to as the degree of dimensional change.

[0071] The degree of dimensional change (α) of the thermoplastic resinfilm (i) of the present invention means the larger of the degrees ofmachine-direction (MD) and transverse-direction (TD) dimensional changesafter heating and cooling (α) as measured by thermomechanical analysisin the range of from room temperature to 135° C. The degree ofdimensional change may be in the range of from −2% (elongation) to 2%(shrinkage) , preferably from −1.5% (elongation) to 1.5% (shrinkage),more preferably from −1.25% (elongation) to 1.25% (shrinkage), even morepreferably from −1% (elongation) to 1% (shrinkage). If the degree ofdimensional change of the film is outside the range of −2% to 2%, thelabel paper curls considerably when printed on a heated-roll fixing typeelectrophotographic printer, which is likely to result in printingtrouble or leads to poor efficiency in peeling the label from therelease paper.

[0072] Degree of Thermal Shrinkage

[0073] The degree of thermal shrinkage after heating at 130° C. for 30minutes of the thermoplastic resin film (i) of the present invention isthe average of the machine-direction and transverse-direction thermalshrinkage values. The degree of thermal shrinkage may be 1.8% or lower,preferably 1.5% or lower, more preferably 1.2% or lower. If the degreeof thermal shrinkage of the film exceeds 1.8%, the label curlsconsiderably when printed on a heated-roll fixing typeelectrophotographic printer.

[0074] The degree of thermal shrinkage may be determined by cutting thefilm into a square shape of a given size, e.g., 100 mm in both lengthand width, measuring the dimensions of the square sample after holdingit in a thermo-hygrostatic chamber having a temperature of 23° C. and arelative humidity of 50%, subsequently heat treating the sample in a130° C. forced-air oven for 30 minutes, taking the film out of theforced-air oven, allowing the film to cool in the samethermo-hygrostatic chamber for 1 hour, and then measuring the dimensionsof the sample.

[0075] Formation of Toner-Receiving Layer

[0076] In order to improve the reception of a toner on the film afterprinting, a toner-receiving layer comprising an inorganic and/or organicpigment and a binder may be formed on the side of the thermoplasticresin film (i) which is to be printed. Any conventional inorganicpigment may be used, such as lightweight or heavy calcium carbonate,clay, titanium oxide, silica, alumina, or the like. In order to improvethe toner reception properties of the film, the thickness of the tonerreception layer may be from 0.1 to 20 μm, preferably in the range offrom 0.5 to 15 μm. The binder may be a polymeric binder such as anacrylic, styrene, or acrylic/styrene polymer, natural rubber, asynthetic rubber, an ethylene/acrylic or ethylene/methacrylic polymer,or a urethane polymer. The binder may have the form of particlesdispersed in water, such as a dispersion or emulsion.

[0077] The toner-receiving layer may be coated on the surface of thethermoplastic resin film (i), for example using a roll coater, bladecoater, bar coater, air-knife coater, gravure coater, reverse coater,die coater, lip coater, spray coater, or the like. The toner-receivinglayer may also be smoothed, as needed. The toner-receiving layer mayalso be dried after coating.

[0078] Pressure-Sensitive Adhesive Layer (ii)

[0079] The type, thickness, and amount of pressure-sensitive adhesivelayer (ii) formed on one side of the thermoplastic resin film (i) may beselected based on the type of adhesive used, the environment in whichthe label paper is expected to be used, the adhesive strength desired,etc.

[0080] A general purpose water- or solvent-based pressure-sensitiveadhesive may be applied and dried to form a pressure-sensitive adhesivelayer. Any pressure-sensitive adhesive, for example those based onnatural rubber, a synthetic rubber, an acrylic, or the like, may beused. Pressure-sensitive adhesives based on a synthetic polymer may beused in the form of a solution in an organic solvent, or in the form ofparticles dispersed in water, such as a dispersion or emulsion.

[0081] A pressure-sensitive adhesive containing a pigment such astitanium white can be used in order to improve the opacity of the label.

[0082] Formation of Pressure-Sensitive Adhesive Layer (ii)

[0083] The pressure-sensitive adhesive layer (ii) may be formed byapplying a solution of a pressure-sensitive adhesive on thesilicone-treated side of a release paper (iii) . The coating may becarried out with a roll coater, blade coater, bar coater, air-knifecoater, gravure coater, reverse coater, die coater, lip coater, spraycoater, or the like. The pressure-sensitive adhesive layer (ii) may alsobe smoothed if needed, and be dried after coating.

[0084] The pressure-sensitive adhesive layer (ii) may also be coateddirectly on the thermoplastic resin film (i).

[0085] Although the pressure-sensitive adhesive layer (ii) may have anysuitable thickness, depending on the intended use of the label, it isusually in the range of from 2 to 30 μm, preferably from 5 to 20 μm.

[0086] Release Paper (iii)

[0087] The release paper (iii) contacts the pressure-sensitive adhesivelayer formed on the thermoplastic resin layer (i), and is generallytreated, on the side in contact with the pressure-sensitive adhesivelayer (ii), with a silicone in order that the release paper may bereadily removed from the pressure-sensitive adhesive layer (ii).

[0088] Any conventional release paper may be used as release paper(iii). For example, the release paper may be silicone-treating wood-freeor kraft paper which has not been pretreated or calendered. In addition,resin coated, film laminated, or silicone-treated glassine paper, coatedpaper, plastic film, or the like, may be used. Paper or film laminatedon both sides with a polymer is effective in reducing curling, becauseit is less influenced by ambient humidity.

[0089] The degree of dimensional change (β) of a release paper may bemeasured under the same conditions as the degree of dimensional changeof the thermoplastic resin film (i) of the present invention, asdetermined by TMA. The degree of dimensional change (β) of a releasepaper means the degree of dimensional change in the machine direction,i.e., the direction (MD) in which the release paper has been wound intoa roll.

[0090] Difference in Degree of Dimensional Change Between ThermoplasticResin Film (i) and Release Paper

[0091] In order to further reduce curling caused by printing on aprinter, the difference (α-β) between the degree of dimensional change(α) of the thermoplastic resin film (i) of the present invention, andthe degree of dimensional change (β) of the release paper as measuredunder the same conditions, may be in the range of from −1.5% to 1.5%,preferably from −1.2% to 1.2%, more preferably from −0.5% to 1%, evenmore preferably from 0% to 0.8%.

[0092] Curling

[0093] The label paper of the present invention is suitable for printingusing a heated-roll fixing type electrophotographic printer. In order toprovide improved the ease of stripping the printed film from the releasepaper, printed A4 label paper (210 mm×297 mm) should have an averagecurl height at the four comers of 50 mm or smaller, preferably 45 mm orsmaller, as measured 2 minutes after the printing.

[0094] Printing

[0095] The thermoplastic resin film (i) of the present invention may beused for any printing method in which heat energy is applied to theprinted surface, such as, e.g., thermal transfer, sublimation transfer,and heat-sensitive printing, and in letterpress printing, gravureprinting, flexography, solvent-based offset printing, andultraviolet-curable offset printing, as well as the base film of a labelprinted using a heated-roll fixing type electrophotographic printingprocess. The thermoplastic resin film (i) or a label paper comprisingsuch a film may be used in the form of a sheet, or in the form of a rollwhen printing with a rotary press. Furthermore, a laminate of thethermoplastic resin film (i) with a release paper may be form printedand then printed on an electrophotographic printer.

[0096] The present invention will be explained in more detail by meansof the following Examples.

[0097] The raw materials and evaluation methods used in the Examples areas follows. The term “parts” in an ingredient blending ratio means“parts by weight”.

EXAMPLE 1

[0098] Thermoplastic Resin Film (i)

[0099] A composition (C) was prepared by compounding polypropylenehaving a melt flow rate (MFR) of 4 g/10 min with 15 wt % heavy calciumcarbonate having an average particle diameter of 1.3 μm, 0.7 wt %titanium white, and 5.5 wt % high-density polyethylene having an MFR of11 g/10 min and was kneaded in an extruder set at 250° C., subsequentlyextruded into a sheet form through a T-die connected to an extruder setat 230° C., and cooled with a cooler to obtain an unstretched sheet.

[0100] Into the above-described composition, and into the resincompositions described in the following Examples and ComparativeExamples, phenolic stabilizers, i.e., 0.05 parts of3-methyl-2,6-di-t-butylphenol and 0.08 parts of Irganox 1010 (tradename; manufactured by Ciba-Geigy Corp.), and 0.05 parts of Weston 618(trade name; manufactured by G. E. Plastics), a phosphorus compoundstabilizer, per 100 parts of the sum of the polypropylene and calciumcarbonate used, were also incorporated. These same stabilizers were alsoused in the compositions of Examples 2 to 4.

[0101] This unstretched sheet was then heated to a temperature of 142°C. and stretched 4.6-fold in the machine direction with amachine-direction stretching machine comprising rolls having differentperipheral speeds.

[0102] A composition (A) was prepared by mixing 43 wt % polypropylenehaving an MFR of 8 g/10 min, 4 wt % maleic-acid-modified polypropylene,and 5% high-density polyethylene (MFR, 10 g/10 min) with 47.5 wt %calcium carbonate having an average particle diameter of 1.3 μm, and 0.5 wt % titanium white and was melt-kneaded in an extruder set at 240°C. A composition (B) was prepared by mixing 47 wt % polypropylene havingan MFR of 11 g/10 min with 47.5 wt % calcium carbonate having an averageparticle diameter of 1.3 μm, 5% high-density polyethylene (MFR, 10 g/10min), and 0.5 wt % titanium white and was melt-kneaded in anotherextruder set at 240° C. The two melts (i.e., compositions (A) and (B))were superimposed in a multilayer coextrusion die, laminated on eitherside of the stretched sheet of composition (C), described above, in sucha manner that the layer of composition (A) faced outward. Thus, afive-layer laminate having the structure A/B/C/B/A was obtained.

[0103] Stretching

[0104] Using a tenter oven, the five-layer laminate described above washeated to 157° C. and then stretched 9.5-fold in the transversedirection. Subsequently, the laminate was passed through a heat-settingzone (set temperature, 163° C.) placed after the tenter oven to obtain afive-layer laminated film having a thickness of 84 μm (thicknesses ofthe individual layers: 5 μm/16 μm/42 μm/16 μm/5 μm)

[0105] Formation of Surface Treatment Layers

[0106] Both sides of this film were subjected to corona dischargetreatment at an applied-energy density of 90 W-min/m².

[0107] Subsequently, an aqueous solution containing a 1:1:1 mixture of abutyl-modified polyethyleneimine, an ethyleneimine adduct of apolyamine-polyamide, and an alkyl acrylate polymer having groupscontaining a quaternary ammonium salt structure was applied to each sideof the film in an amount of about 0.1 g/m² (based on the weight of thedry film), and the coating was dried to form surface treatment layers oneither side of the multilayer thermoplastic resin film.

[0108] Heat Treatment

[0109] The film (i), obtained as described above, was heat-treated for 2days in a forced-air oven set at 110° C.

[0110] Measurement of Degree of Dimensional Change

[0111] The degree of dimensional change of the film (i), describedabove, was measured in the following manner. A “TMA120C” TMA apparatus,manufactured by Seiko Instruments Inc., was used in the tension mode. Afixed load of 5.25 g was used (tension per unit area, 15.625 g/mm²; theload was selected so as to be proportional to the film thickness, withthe tension constant). A film sample was prepared so that the portion ofthe sample examined had a width of 4 mm and a length of 10 mm (theportions of the sample clamped to the upper and lower parts of the TMAwere each 5 mm long). The rate of both heating and cooling during themeasurement was 2° C./min. The temperature range over which the samplewas measured was from 40° C. to a set temperature of 150° C. (actualtemperature, 135° C.), and then the sample was cooled to roomtemperature. The degree of MD dimensional change (α) was 0.59%.

[0112] Property Measurement

[0113] The basis weight of the thermoplastic resin film (i) of thepresent invention had a basis weight and a density, measured inaccordance with JIS-P8118-1976, of 71 g/m² and 0.85 g/m³, respectively,and an opacity, measured in accordance with JIS-P8138-1976, of 91%. Inaddition, it had a porosity of 31%.

[0114] Formation of Toner-Receiving Layer

[0115] A toner-receiving layer was formed on one side of the film (i)using about 10 g/m² of a coating prepared as described below.

[0116] To 100 g of water were successively added 40 parts of BrilliantS-15 (trade name; precipitated calcium carbonate pigment; 50 wt %aqueous dispersion; manufactured by Shiraishi Kogyo Kaisha, Ltd.), 10parts of a 50 wt % aqueous dispersion of Ultra White 90 (trade name;clay pigment; manufactured by Engelhard, Ltd.), 45 parts of Mobinyl M735(trade name; acrylic emulsion; solid content on dry basis, 43 wt %;manufactured by Hoechst Gosei K. K.), and 5 parts of a 15 wt % aqueoussolution of Z-100 (trade name; modified poly(vinyl alcohol) ;manufactured by The Nippon Synthetic Chemical Industry Co., Ltd.) andstirred at room temperature for 2 hours to prepare a coating fluid.

[0117] This coating fluid was applied to one side of the film (i) with abar coater in an amount of about 10 g/m² on a dry basis. The coated filmwas dried for 2 minutes in a 105° C. forced-air oven, removed, and thenallowed to stand at room temperature for 4 hours. A pressure-sensitiveadhesive and a release paper were subsequently applied to this coatedfilm.

[0118] Formation of Pressure-Sensitive Adhesive Layer and Application ofRelease Paper

[0119] 6 g/m² (dry basis) of a solvent-based acrylic pressure-sensitiveadhesive was applied to a silicone treated clay-coated paper releasepaper (iii) using a comma coater. Hereinafter, this release paper willbe referred to as “release paper 1”. The coating was dried to form apressure-sensitive adhesive layer (ii). This release paper was appliedto the thermoplastic resin film (i), having the toner-receiving layerdescribed above, to obtain a label paper. The pressure-sensitiveadhesive layer (ii) was disposed between the release paper (iii) and thesurface of the thermoplastic resin film (i) which was not coated withthe toner-receiving layer.

[0120] The degree of MD dimensional change (β) of the release paper usedwas measured under the same conditions as for the thermoplastic resinfilm (i), and was 0.18% (shrinkage).

[0121] Evaluation

[0122] The label, prepared as described above, was cut into A-4 (210 mmin width direction by 297 mm in flow direction). The cut label wasallowed to stand in a thermo-hygrostatic chamber at temperature of 23°C. and a relative humidity of 50% for 1 day and then printed on acommercial heated-roll fixing type electrophotographic printer (LaserShot 404G2; trade name; manufactured by Canon Inc.). The printing sideof the label paper faced downward.

[0123] After being printed, the label was allowed to stand at roomtemperature on a flat table and the average of the curl heights at thefour corners was determined 2 minutes after printing. The average of thecurl heights was 34 mm.

[0124] Test printing of these labels was also carried out, and the printquality was visually evaluated. If the print quality of the labels wasequivalent to the print quality obtained on a commercial PPC paper mademainly of a bleached chemical pulp, the print quality was consideredsatisfactory (O). If the printing had noticeable defects such as linewidth increase or deformation of printed characters, scumming, andinsufficient printing density, the print quality was considered poor(X). The print quality of the label prepared as described above inExample 1 was considered satisfactory. The results of the evaluation ofthe label of Example 1 are shown in Table 1.

COMPARATIVE EXAMPLE 1

[0125] Labels were prepared according to the procedure of Example 1,except that the heat treatment of the thermoplastic resin film (i) in aforced-air oven was omitted. The label was evaluated as described inExample 1, and the results are shown in Table 1

EXAMPLE 2

[0126] A five-layer laminated thermoplastic resin film (i) having athickness of 118 μm (thicknesses of the individual layers: 5 μm/25 μm/58μm/25 μm/5 μm) was prepared using the procedure of Example 1, exceptthat the thickness of some of the individual film layers is slightlydifferent. The thermoplastic resin film obtained was treated for 2 daysin a forced-air oven set at 110° C.

[0127] The same surface treatment and the same pressure-sensitiveadhesive and release paper as in Example 1 were applied to produce alabel paper which was evaluated as described in Example 1. The resultsare shown in Table 1.

EXAMPLE 3

[0128] A composition (C′) was prepared by compounding polypropylenehaving a melt flow rate (MFR) of 4 g/10 min with 15 wt % heavy calciumcarbonate having an average particle diameter of 1.3 μm, 0.7 wt %titanium white, and 5.5 wt % high-density polyethylene having an MFR of11 g/10 min was kneaded in an extruder set at 250° C., subsequentlyextruded in a sheet form using a T-die connected to an extruder set at230° C., and cooled with a cooler to obtain an unstretched sheet.

[0129] This unstretched sheet was heated to a temperature of 148° C. andstretched 4.6-fold in the machine direction with a machine-directionstretching machine comprising rolls having different peripheral speeds.

[0130] A composition (A′) was prepared by mixing 45 wt % polypropylenehaving an MFR of 10 g/10 min, 5 wt % maleic-acid-modified polypropylene,and 5% high-density polyethylene (MFR, 10 g/10 min) with 44.5 wt %calcium carbonate having an average particle diameter of 1.3 μm and 0.5wt % titanium white and melt-kneading the mixture in an extruder set at250° C. A composition (B′) was prepared by mixing 47 wt % polypropylenehaving an MFR of 11 g/10 min with 47.5 wt % calcium carbonate having anaverage particle diameter of 1.3 μm, 5% high-density polyethylene (MFR,10 g/10 min), and 0.5 wt % titanium white and melt-kneaded the mixturein another extruder set at 240° C. The two melts (i.e., compositions(A′) and (B′)) were superimposed in a multilayer coextrusion die,laminated on either side of the stretched sheet of composition (C′),described above, in such a manner that the layer of composition (A′)faced outward. Thus, a five-layer laminate having the structureA′/B′/C′/B′/A′ was obtained.

[0131] Stretching

[0132] The five-layer laminate described above was heated to 158° C. ina tenter oven, and then stretched 9.5-fold in the transverse direction.Subsequently, the laminate was passed thlrouh a heat-setting zone (settemperature, 175° C.) located after the tenter oven to obtain afive-layer laminated film having a thickness of 84 μm (thicknesses ofthe individual layers: 5 μm/17 μm/40 μm/17 μm/5 μm).

[0133] The same procedure was carried out as in Example 1, except thatthe treatment of the film in a forced-air oven was omitted.

[0134] Thus, a pressure-sensitive adhesive and a release paper wereapplied to produce a label paper. This label paper was evaluated, andthe results are shown in Table 1.

EXAMPLE 4

[0135] A composition (D′) was prepared by compounding polypropylenehaving a melt flow rate (MFR) of 4 g/10 min with 15 wt % heavy calciumcarbonate having an average particle diameter of 1.3 μm, 5 wt %high-density polyethylene having an MFR of 10 g/10 min, and 0.7 wt %titanium white, then kneaded the composition in an extruder set at 250°C., extruding the composition into strands, then pelletizing thestrands.

[0136] A three-layer T-die was connected to two extruders. The extruderused to provide the polymer melt for the central layer of the T-die wasset at 240° C., and the extruder used to provide polymer melt for theoutside layers of the T-die was set at 250° C. The composition (D′) wasextruded from the extruder supplying the central layer of the T-die, anda composition (E′) containing a polypropylene having an MFR of 4 g/10min, 10 wt % calcium carbonate with an average particle diameter of 1.3μm and 0.7 wt % titanium white was extruded from the extruder supplyingthe exterior layers of the T-die, thereby providing an extruded sheethaving a three-layer structure, E′/D′/E′. This extruded sheet was cooledwith a cooler to provide an unstretched three-layer laminated sheet.

[0137] This unstretched sheet was heated to a temperature of 142° C. andstretched 4.8-fold in the machine direction with a machine-directionstretching machine comprising rolls having different peripheral speeds.

[0138] This five-layer laminate was heated to 157° C. and then stretched9.5-fold in the transverse direction using a tenter oven.

[0139] The stretched laminate was then passed through a heat-settingzone (set temperature, 170° C.) located after the tenter oven to providea three-layer laminated film base (i) having a thickness of 78 μm(thicknesses of the individual layers: 8 μm/62 μm/8 μm).

[0140] The thermoplastic resin film then heat-treated for 3 days in aforced-air oven set at 110° C.

[0141] The thermoplastic resin film was then subjected to the samesurface treatment, application of a pressure-sensitive adhesive and arelease paper as described in Example 1, thereby providing a labelpaper. The label paper was evaluated, and the results are shown in Table2.

EXAMPLE 5

[0142] The production of a thermoplastic resin film (i), formation of atoner-receiving layer, formation of a pressure-sensitive adhesive layer,and application of a release paper were conducted by conducting the sameprocedure as in Example 1, except that the release paper used was arelease paper (iii) having a thickness of 120 μm and a density of 1.1g/m² obtained by treating a clay-coated paper with a silicone(hereinafter abbreviated as release paper 2). Thus, a label paper wasobtained.

[0143] The degree of MD dimensional change (P) of the release paper usedwas measured under the same conditions as for the thermoplastic resinfilm (i). As a result, it was −0.1% (elongation).

[0144] The results of evaluation are shown in Table 1.

COMPARATIVE EXAMPLE 2

[0145] The same procedure as in Comparative Example 1 was conducted,except that the same release paper as in Example 5 was used. Thus, alabel paper to which a pressure-sensitive adhesive and the release paperhad been applied was produced. This label paper was evaluated. Theresults are shown in Table 1. TABLE 1 Comparative Comparative Example 1Example 1 Example 2 Example 3 Example 4 Example 5 Example 2Thermoplastic resin film base (i) Thickness (μm) 84 84 118  84 78 84 84Basis weight (g/m²) 71 64 99 83 59 71 64 Density (g/cm³) 0.85 0.76 0.840.99 0.76 0.85 0.76 Porosity (%) 31 33 32 12 30 31 33 Opacity (%) 91 9192 72 74 91 91 Degree of dimensional change α by 0.6  3.1  0.57 −0.3 0.55 0.6  3.1  thermomechanical analysis (%) Degree of thermal shrinkage(%), 0.82 2.1  0.8  0.7  0.75 0.82 2.1  130 EC, 30 min Kind of releasepaper used release paper release paper release paper release paperrelease paper release paper release paper 1 1 1 1 1 1 1 Degree ofdimensional change β of release paper 0.18 0.18 0.18 0.18 0.18 −0.1 −0.1  by thermomechanical analysis (%) Difference in degree ofdimensional 0.42 2.92 0.39 −0.48  0.37 0.7 3.2  change bythermomechanical analysis between base (i) and release paper, α − β (%)Results of print evaluation Curl height (mm), 2 min after printing 35Cylinder 33 33 32 38 cylinder Print quality ◯ ◯ ◯ ◯ ◯ ◯ ◯

[0146] As apparent from Table 1 above, same effect is obtained by eitherof the two means specified in the invention, i.e., the degree ofdimensional change (a) and the degree of thermal shrinkage.

EXAMPLE 6

[0147] Thermoplastic Resin Film (i)

[0148] A composition (C′) prepared by compounding 79.4 wt % propylenehomopolymer having a melt flow rate (MFR) of 3.3 g/10 min with 15 wt %heavy calcium carbonate having an average particle diameter of 1.5 μm,0.6 wt % titanium white, and 5 wt % high-density polyethylene having anMFR of 10 g/10 min was kneaded with an extruder set at 250° C.,subsequently extruded into a sheet form through a T-die connected to anextruder set at 240° C., and cooled with a cooler to obtain anunstretched sheet.

[0149] Into the above-described composition to be extruded in sheet formand into the following compositions to be extruded and laminated and thecompositions used in the following Examples were incorporated 0.05 partsof 3-methyl-2, 6-di-t-butylphenol, 0.05 parts of Irganox 1010 (tradename; manufactured by Ciba-Geigy Corp.) as a phenolic stabilizer, and0.05 parts of Weston 618 (trade name; manufactured by G. E. Plastics) asa phosphorus compound stabilizer per 100 parts of the sum of thepropylene homopolymer and calcium carbonate used.

[0150] This sheet was heated to a temperature of 142° C. and stretched4.5-fold in the machine direction with a machine-direction stretchingmachine comprising rolls having different peripheral speeds.

[0151] A composition (A′) prepared by mixing 46 wt % propylenehomopolymer having an MFR of 8 g/10 min, 4 wt % maleic-acid-modifiedpolypropylene, and 5% high-density polyethylene (MFR: 10 g/10 min) with44.4 wt % calcium carbonate having an average particle diameter of 1.5μm and 0.6 wt % titanium white was melt-kneaded with an extruder set at240° C. A composition (B′) prepared by mixing 49.4 wt % propylenehomopolymer having an MFR of 10 g/10 min with 45 wt % calcium carbonatehaving an average particle diameter of 1.5 μm, 5% high-densitypolyethylene (MFR: 10 g/10 min), and 0.6 wt % titanium white wasmelt-kneaded with another extruder set at 240° C. The two melts weresuperposed within a die, and laminated by coextrusion to each side ofthe stretched sheet obtained by extruding the resin composition (C′)described above and stretching the extrudate 4.5 times in the machinedirection, in such a manner that (A′) faced outward. Thus, a five-layerlaminate (A′/B′/C′/B′/A′) was obtained.

[0152] Stretching

[0153] Using a tenter oven, the five-layer laminate described above washeated to 157° C. and then stretched 9.4-fold in the transversedirection. Subsequently, the laminate was passed through a heat-settingzone (set temperature, 168° C.) located after the tenter oven to obtaina five-layer laminated film having a thickness of 80 μm (thicknesses ofthe individual layers: 5 μm/15 μm/40 μm/15 μm/5 μm).

[0154] Formation of Surface Treatment Layers

[0155] Both sides of this film were subjected to corona dischargetreatment at an applied-energy density of 90 W min/m².

[0156] Subsequently, an aqueous solution containing a 1:1:1 mixture of abutyl-modified polyethyleneimine, an ethyleneimine adduct of apolyamine-polyamide, and an alkyl acrylate polymer having groupscontaining a quaternary ammonium salt structure and represented by thefollowing structural formula, in the molecular chain was applied to eachside of the film in an amount of about 0.1 g/m² on a dry basis, and thecoating was dried to form surface treatment layers.

[0157] Heat Treatment

[0158] This film (i) was cut into a B-4 size and heat-treated for 1 hourin a forced-air oven set at 110° C.

[0159] Property Measurement

[0160] This film (i) was cut into a square shape of 100 mm in each oflength and width, and the dimensions thereof were measured with acathetometer in a thereto-hygrostatic chamber having a temperature of23° C. and a relative humidity of 50%. Thereafter, the cut film washeat-treated in a 130° C. forced-air oven for 30 minutes, taken outtherefrom, and then allowed to cool in the same thereto-hygroscopicchamber for 1 hour. The dimensions thereof were measured. The degree ofshrinkage was calculated by comparison with the dimensions measuredbefore the oven heat treatment. As a result, the degree ofmachine-direction shrinkage was 1.0%, that of transverse-directionshrinkage was 0. 6%, and the average was 0.8%. The film had a basisweight and a density as measured in accordance with JIS-P8118-1976 of68.4 g/m² and 0.85 g/cm³, respectively. It further had a porosity of31%.

[0161] Formation of Toner-Receiving Layer

[0162] A toner-receiving layer was formed on one side of the film (i) bycoating in an amount of about 10 g/m² by conducting the same procedureas in Example 1.

[0163] This film was used in the subsequent application of apressure-sensitive adhesive and a release paper thereto.

[0164] Application of Pressure-Sensitive Adhesive and Release Paper

[0165] A solvent-based acrylic pressure-sensitive adhesive was appliedto a release paper (iii) having a thickness of 115 μm and a density of1.2 g/m² obtained by treating a clay-coated paper with a silicone(hereinafter abbreviated as coat type) on the silicone-treated side witha bar coater in an amount of 8 g/m² on a dry basis. The coating wasdried to form a pressure-sensitive adhesive layer (ii). This releasepaper was applied to the plastic resin film (i) having thetoner-receiving layer described above to obtain a label paper.

[0166] Evaluation

[0167] The label paper obtained was cut into A-4 (210 mm in width by 297mm in flow). The cut label was allowed to stand in a thermo-hygrostaticchamber of 23° C. and a relative humidity of 50% for 1 day and thenprinted on a commercial heated-roll fixing type electrophotographicprinter (Laser Shot 404G2; trade name; manufactured by Canon Inc.), inwhich paper passed with its printing side facing upward.

[0168] After having been printed on the printer, the label was allowedto stand at room temperature on a flat table and the average of the curlheights at the four comers was determined at 2 minutes after theprinting. As a result, the average was found to be 39 mm.

[0169] Test printing was conducted in a test printing and the printquality was visually evaluated. The prints which were equal in printquality to a print obtained by printing a commercial PPC paper mademainly of a bleached chemical pulp are regarded as satisfactory (O),while those which had noticeable defects such as line width increase ordeformation of printed characters, scumming, and printing densityinsufficiency are regarded as poor (X). Example 6 was on a satisfactorylevel. The results of the evaluation of Example 6 are shown in Table 2.

COMPARATIVE EXAMPLE 3

[0170] The same procedure as in Example 6 was conducted, except that theheat treatment was omitted. Thus, a pressure-sensitive adhesive and arelease paper were applied to produce a label paper, and this labelpaper was evaluated. The results are shown in Table 2.

COMPARATIVE EXAMPLE 4

[0171] The same procedure as in Example 6 was conducted, except thatsynthetic paper Yupo FPG-80 (trade name; manufactured by Oji-YukaSynthetic Paper Co., Ltd.) was used as a thermoplastic resin film. Thus,a pressure-sensitive adhesive and a release paper were applied toproduce a label paper, and this label paper was evaluated. The resultsare shown in Table 2.

EXAMPLE 7 TO EXAMPLE 9

[0172] The same procedure as in Example 6 was conducted, except that theheat treatment in the forced-air oven was conducted for time periods of0.5 hours, 4 hours, and 168 hours. The results of evaluation are shownin Table 2.

EXAMPLE 10

[0173] The same procedure as in Example 6 was conducted, except that theheat treatment in the forced-air oven was conducted at a temperature of130° C. The results of evaluation are shown in Table 2.

EXAMPLE 11

[0174] The same procedure as in Example 6 was conducted, except that theheat treatment in the forced-air oven was conducted at a temperature of105° C. for a time period of 24 hours. The results of evaluation areshown in Table 2.

EXAMPLE 12

[0175] A composition (C′) prepared by compounding 79.4 wt % propylenehomopolymer having a melt flow rate (MFR) of 3.3 g/10 min with 15 wt %heavy calcium carbonate having an average particle diameter of 1.5 μm,0.6 wt % titanium white, and 5 wt % high-density polyethylene having anMFR of 10 g/10 min was kneaded with an extruder set at 250° C.,subsequently extruded into a sheet form through a T-die connected to anextruder set at 240° C., and cooled with a cooler to obtain anunstretched sheet.

[0176] This sheet was heated to a temperature of 147° C. and stretched4.4-fold in the machine direction with a machine-direction stretchingmachine comprising rolls having different peripheral speeds.

[0177] A composition (A′) prepared by mixing 46 wt % propylenehomopolymer having an MFR of 8 g/10 min, 4 wt % maleic-acid-modifiedpolypropylene, and 5% high-density polyethylene (MFR: 10 g/10 min) with44.4 wt % calcium carbonate having an average particle diameter of 1.5μm and 0.6 wt % titanium white was melt-kneaded with an extruder set at240° C. A composition (B′) prepared by mixing 49.4 wt % propylenehomopolymer having an MFR of 10 g/10 min with 45 wt % calcium carbonatehaving an average particle diameter of 1.5 μm, 5% high-densitypolyethylene (MFR: 10 g/10 min), and 0.6 wt % titanium white wasmelt-kneaded with another extruder set at 240 EC. The two melts weresuperposed within a die, and laminated by coextrision to each side ofthe stretched sheet obtained by extruding the resin composition (C′)described above and stretching the extrudate 4.5 times in the machinedirection in such a manner that (A′) faced outward. Thus, a five-layerlaminate (A′/B′/C′/B′/A′) was obtained.

[0178] Stretching

[0179] Using a tenter oven, the five-layer laminate described above washeated to 160° C. and then stretched 9-fold in the transverse direction.Subsequently, the laminate was passed through a heat-setting zone (settemperature, 168° C.) located after the tenter oven to obtain afive-layer laminated thermoplastic resin film (i) having a thickness of132 μm (thicknesses of the individual layers: 6 μm/27 μm/66 μm/27 μm/6μm). The thermoplastic resin film obtained was cut into a B-4 size andtreated for 2 hours in a forced-air oven set at 110° C.

[0180] The same heat treatment and the same application of apressure-sensitive adhesive and a release paper as in Example 6 wereconducted to produce a label paper, which was evaluated. The results areshown in Table 3.

COMPARATIVE EXAMPLE 5

[0181] The same procedure as in Example 13 was conducted, except thatthe heat treatment was omitted. Thus, a pressure-sensitive adhesive anda release paper were applied to produce a label paper, and this labelpaper was evaluated. The results are shown in Table 3.

EXAMPLE 14

[0182] The same procedure as in Example 6 was conducted, except that aheat treatment was conducted in such a manner that the thermoplasticresin film was wound into a roll and the front and back sides of thefilm were successively brought into contact with four metal rolls set at120° C. while regulating the contact time to about 4 minutes. Theresults of evaluation are shown in Table 3. TABLE 2 Example ComparativeComparative Example Example Example Example Example 6 Example 3 Example4 7 8 9 10 11 Thermoplastic resin film base (i) Thickness (μm) 80 80 8080 80 80 80 80 Basis weight (g/m²) 68.4  68.4  61.6  68.4  68.4  68.5 68.5  68.5  Density (g/m³)  0.85  0.85  0.77  0.85  0.85 0.85 0.85 0.85Porosity (%) 31 31 33 31 31 31 31 31 Opacity (%) 90 90 90 90 90 90 90 90Conditions of heat treatment Temperature (EC) 110 none none 110  110 110  130  105  Time (hr)  1 none none 0.5  4 168   1 24 Degree ofthermal shrinkage of (i) (%), 130 EC, 0.8 2.2 2.3  0.82 0.8 0.79 0.780.82 30 mm Thickness after toner-receiving layer formation 88 88 88 8888 88 88 88 (μm) Opacity after toner-receiving layer formation (%) 92 9292 92 92 92 92 92 Kind of release paper used coat type coat type coattype coat type coat type coat type coat type coat layer Results of printevaluation Curl height (mm), 2 min after printing 39 cylinder cylinder42 40 38 37 42 Print quality (visual examination) ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯

[0183] TABLE 3 Example Example Comparative Example 12 13 Example 5 14Thermoplastic resin film base (i) Thickness 132 80 80 80 (μm) Basicweight 133 64 64 68.4 (g/m²) Density (g/cm³) 1.01 0.8 0.8 0.85 Porosity(%) 12 19 19 31 Opacity (%) 84 82 82 90 Conditions of heat treatmentsTemperature 110 110 none 120 (EC) Time (hr) 2 2 none about 4 min Degreeof 0.5 0.69 2.1 0.82 thermal shrinkage of (i) (%), 130EC, 30 minThickness after 138 88 88 88 toner-receiving layer formation (μm)Opacity after 90 89 89 92 toner-receiving layer formation (%) Kind ofrelease coat type coat type coat type coat type paper used Results ofprint evaluation Curl height 33 35 68 41 (mm), 2 min after printingPrint quality O O O O (visual examination)

[0184] Industrial Applicability of the Invention

[0185] As described above, according to the invention, a thermoplasticresin film, in particular, a polypropylene-based film, could be obtainedwhich had suitability for heated-roll fixing type electrophotographicprinters and was especially satisfactory in curling after printing.

[0186] Furthermore, a label paper employing the same could be obtained.

[0187] Since the thermoplastic resin film obtained according to theinvention and the label paper employing the same are superior toplain-paper labels in strength and water resistance, they are useful asstickers for outdoor advertisement, labels for frozen-food containers,or namers (labels showing usage or notice) for industrial products.

1. A thermoplastic resin film (i) comprising a stretched thermoplasticresin sheet comprising a thermoplastic resin, wherein the thermoplasticresin film has a degree of dimensional change after heating and cooling(α) in the range of from −2% to 2% as measured by thermomechanicalanalysis in the range of from room temperature to 135° C. or which has adegree of thermal shrinkage of 1.8% or lower upon heating at 130° C. for30 minutes or longer.
 2. The thermoplastic resin film (i) according toclaim 1 , having a degree of dimensional change after heating andcooling (α) in the range of from −2% to 2% as measured bythermomechanical analysis in the range of from room temperature to 135°C.
 3. The thermoplastic resin film (i) according to claim 1 , having adegree of thermal shrinkage of 1.8% or lower upon heating at 130° C. for30 minutes or longer.
 4. The thermoplastic resin film (i) according toclaim 1 , having a degree of dimensional change after heating andcooling (α) in the range of from −2% to 2% as measured bythermomechanical analysis in the range of from room temperature to 135°C., and having a degree of thermal shrinkage of 1.8% or lower uponheating at 130° C. for 30 minutes or longer.
 5. The thermoplastic resinfilm (i) according to any one of claims 1 to 4 , comprising from 35 to100 wt % of a thermoplastic resin and from 65 to 0 wt % of inorganicand/or organic fine particles.
 6. The thermoplastic resin film (i)according to any one of claims 1 to 5 , wherein the thermoplastic resinis a porosity as shown by the following equation of from 8 to 60%:${{Porosity}\quad (\%)} = {\frac{\rho_{0} - \rho}{\rho_{0}} \times 100}$

ρ₀: density of the resin film before stretching ρ: density of the resinfilm after stretching.
 7. The thermoplastic resin film (i) according toany one of claims 1 to 6 , wherein the thermoplastic polyolefin resin isa polyolefin-based resin.
 8. The thermoplastic resin film (i) accordingto claim 7 , wherein the polyolefin-based resin is a polypropylene-basedresin.
 9. The thermoplastic resin film (i) according to any one ofclaims 6 to 8 , which has an opacity as measured in accordance withJIS-P8138-1976 of from 20% to 100%.
 10. The thermoplastic resin film (i)according to any one of claims 1 to 9 , which is one obtained through aheat treatment.
 11. The thermoplastic resin film (i) according to claim10 , wherein the heat treatment is carried out at 90° C. to 250° C. 12.The thermoplastic resin film (i) according to claim 10 or 11 , whereinthe heat treatment is carried out in an oven.
 13. The thermoplasticresin film according to any one of claims 1 to 12 , which comprises atoner receiving layer on one side thereof.
 14. The thermoplastic resinfilm according to any one of claims 1 to 13 , which comprises a tonerreceiving layer on at least the side thereof opposite to the side incontact with a pressure-sensitive adhesive layer.
 15. A label paperwhich comprises a thermoplastic resin film (i), a pressure-sensitiveadhesive layer (ii), and a release payer (iii), in this order on thethermoplastic resin film (i), wherein the thermoplastic resin film (i)is the thermoplastic resin film (i) according to any one of claims 1 to14 .
 16. The label paper according to claim 15 , wherein a A-4 size (210mm×297 mm) paper has an average curl height at the four corners of 50 mmor smaller, measured 2 minutes after printing the label paper with aheated-roll fixing type electrophotographic printer.
 17. The label paperaccording to claim 15 or 16 , wherein the thermoplastic resin film (i)has a degree of dimensional change after heating and cooling (α) in therange of from −2% to 2% as measured by thermomechanical analysis in therange of from room temperature to 135° C., and the difference (α-β)between the degree of dimensional change (α) of the film and the degreeof dimensional change after heating and cooling (β) of the release paper(iii), as measured by thermomechanical analysis in the range of fromroom temperature to 135° C., is in the range of from −1.5% to 1.5%.